Here are a couple of pictures of the speaker cans that came with my boat:

The dark marks are where the salt broke through the clear coat and got down to the aluminum underneath. On my speakers once this happens then you can't really polish it out. It's just cosmetic and unless I point it out no one really notices. I haven't had any of the electronics fail because of the previous salt water use. My boat does have zincs on the rudder, shaft and heat exchangers. The salt water boats in 2006 had these upgraded wiring, stainless hardware, built in flush kit and raw water strainer.